Excel – Vista problems

Hi all,
I have a strange issue with vista and Excel. I have a user with a PC with Vista Business and office 2003 sp3; and I have a shared folder in a W2003 R2 server.
When she try to save an excel workbook receive a message of ?Sharing violation? and Excel creates another file instead of save the changes.
All the XP user don?t have any problem and if she log in on a XP machine doesn?t have the problem.
Just for test I make her owner of the workbook and gave her full control over the folder and still the same problem.
Ideas? suggestion? please? 